Control system



Oct. 11, 1949. J. F. YOUNG 2,484,262

CONTROL SYSTEM .Origihal Filed 001:. 8, 1945 Fig.4.

Field Flux WITNESSES: Time INVENTOR James F. Young I ME WMMVQ ATTORNEY Fieid Volfs Patented Oct. 11, 1949 CONTROL SYSTEM,

James Young, Pittsburgh, Pa., assignon to:

WestinghouseElectric Corporation, East Huts-- burgh, Pa, a} corporation lof; Iiennsylvania;

Original application October 8'; 1945; Serial No.

621,077. Divided and thisa-pplica-tion October 12, 1948; Serial No. 54,034

8 Claims.

This invention relates'to generator, control systems and more particularly to systems which control the. rate of discharge of generator fields.

This applicationislamdivisionof the copending. applicationofElmer G; Ratz', Serial No. 621,077, filed October 8-, 1945, entitled Meansto open generator field circuit and to dissipate stored magnetic field energy.

Numerous efforts havebeen made in thepastto minimize. the efiect of faults ongenerators. Most of these, however, provide only for; extremely fast disconnection of the generator from its loadand the disconnectionof its field circuits. This, in most cases, does not have maximum effectiveness since the self-induced E. M. F. of the generator, requiressome time to drop due, to the relatively. slow decay of the field fiuX. Shoulda generator, be faulted, for example, in one of itsarmature, windings, it is extremely important thatthe field fiux be reduced to a negligible value, and preferably to zero, as quickly as possible to eliminate the self-generated voltage, for the reason that'the. self-generated voltage causes damage atthe point: where the generator is faulted as long as it exists. In the usual case, for example, it has been found that in large machines 8 to 20 seconds may berequiredfor the complete discharge of afield cir cuit having a fixed resistance. This invention provides means whereby the field dischargetime' may be reduced, if desired, to one second 01 less.

Protective relays which operate inone cycle or less are now 'utilized'to sense fault conditions and" trip out the switches connecting the generator field to its energizing source and the armatureto theload circuits; but the gain'in speed-of'such relays is largely ineffective as far as theself-g-enerated E. M. F. of the generator is concerned. In other words the gain of -or B cycles in faultsensing relay operation over some of the early types is of little value in view of theslow decay of the generator field flux. In the ordinary case, the field discharge resistor is made asv highin. ohmic value as the fieldinsulationwill.permiti Obviously the higher the discharge resistance ithe; quicker the field flux will decay. As soon as the generator is disconnected from. its load circuits. and the field switch is opened to disconnect the field from its energizing source and to; connect the discharge resistor across the field, the decays ing field flux of the generator, due to the change in flux, generates a self-induced E. M. F. inthe field and this E. M. F. discharges gradually. through the discharge resistor The higher; the ohmic value of the discharge. resistor the greater. the selfeinduced voltage will be, and,,therefore;,

thelmorerapid thezdecay. of the field flux. The

limit;.,oii course,- is.=.determined,hy. the voltage the,

field windings; may withstand withoutpuncturing the. insulation.

This,=,invention .has for its object the provision of 1a.: control .for; aygenerator, whereby the decay; of: the". generator. field flux isasirapid aspossible:

when the generatorfieldis connectedwith its discharge circuit.

More aspecificallyi stated; the, object of this ,in-.

vention .is;to.increase the resistance of the field Figsn31'and4 embrace the principles of Fig. 1,

bututilize different resistor; control elements,

Eig-; 5:graphicallyillustratesthe rate of decay. ofthegfieldfiux obtainable with the modifications ofthe inventionin Figs. 1 through las compared Withithestandardfixed resistor type, of discharge circuit, and

Figyfi similarly compares the discharge volt-..

ages.

three. current-responsive automatic relays ICA,

Midland- 36A, each responsive to-the differentials of the currents= in. the. circuits on opposite sides OfiOl'lGOif the.generatorarmature windings and: having their contact elements eachiconnected .in-

energizing circuits forv the coil: of the tripping solenoids TS]: of; the mainswitch MS and T32:

of the field switch-,Esg'and a field-discharge conetrol arrangement: including the carbon pile resistor R controlled-by the solenoids which is re-- sponsive to the voltage ;of field'fi'.

Each of. the current-responsive automatic res lays ICA, ZGA and3CA-a11e energized; by, the, differential of theelectrical outputs oflapair-OL current transformers, respectively, energized by the currents on opposite sides of each of the generator armature windings. The outputs of each pair of current transformers are in opposition in the associated automatic relay in the manner well known to the art. The automatic relays are preferably of the type which respond extremely fast to a current differential which may result, for example, from a grounding of an armature winding on the armature iron. Any one of the automatic relays upon closing its contacts completes an energizing circuit for the coils of the tripping solenoids TS! and TSZ.

The control for the field switch FS and the main switch MS is represented in block diagram. It will be understood, however, that such a control includes a conventional arrangement of push buttons and other control devices for efiecting proper operation of the system. As illustrated, the main switch and field switch are in their operated positions and thus the armature winding is connected to its load circuits and the field winding connected to its energizing source.

Should a fault occur on any one of the generator armature windings, the associated currentresponsive automatic relay is operated to immediately actuate the tripping solenoids TSI and TS2 thus simultaneously tripping out the main switch and the field switch. The main switch disconnects the armature windings from the load circuits. In dropping out, the field switch FS opens its contacts FSI in the energizing circuit for the tripping solenoid TS2 and at its makebefore-break contacts FS'Z it opens the energizing circuit for the field winding F and connects the discharge circuit including the carbon pile resistor R and the coil of solenoid S thereacross.

The field discharge voltage controls the solenoid S which, in turn, controls the pressure applied to the carbon pile resistance element R. Movements of the plunger of the solenoid are transmitted through a bell crank to one extremity of the carbon pile resistor R1, the mechanical arrangement being such that energization of the solenoid coil increases the pressure applied to the carbon pile resistor. A tension spring affixed to the bell-crank extremity bearing against the carbon pile resistor, opposes bell-crank movements caused by the solenoid. Thus when the back contacts or" the contact assembly FS2 connect the carbon pile resistor R and the solenoid coil S across the field circuit there results an action graphically explained in Figs. 5 and 6 by the dotted curves. At the first instant when the discharge voltage is high the solenoid applies maximum pressure to the carbon pile assembly. Hence, its resistance is a minimum value. As the voltage drops the solenoid pull diminishes and the tension spring functions to relieve the pressure on the carbon pile thus increasing its resistance. Thus the field flux and voltage as a consequence of the gradual insertion of discharge resistance are reduced to a minimum value in a very short time as a comparison of the dotted curves with the full line curves representative of a fixed resistance depicts.

A variant of the arrangement of Fig. 1 is had in Fig. 2 wherein the solenoid is time delayed bymeans of the dashpot D and is energized from a separate source through the contacts of the voltage relay VR, which relay is energized by connection of its coil across the discharge circuit at the back contacts of the assembly FS2. In this arrangement the bell crank is reversed and the solenoid now relieves the pressure on the carbon pile element R, the maximum pressure and hence minimum resistance thereof for initial field discharge now being determined by the compression spring at the carbon pile extremity of the bell crank, which spring biases the bell crank oppositely to movements thereof caused by the solenoid. The dotted curves of Figs 9 and 10 apply here also. In the first instant of field discharge the fiux is high and an instant thereafter th voltage also peaks. Relay V'R thus responds and energizes the coil of the solenoid S from its separate energizing source. Movement of the solenoid plunger is limited to a predetermined rate by the dashpot D to some optimum value that the maximum discharge resistance which may be had without causing excessive discharge voltage peaks is inserted in the discharge circuit.

The electrical equivalent of the invention shown in Fig. 1 appears in Fig. 3. In this arrangement a spring contact regulator SR has the flexible conductors FC thereof connected along spaced taps of the resistor R2 added in the field discharge circuit, the resistor RI as in Figs. 1 and 2 being the fixed maximum value the field winding insulation will permit. The free extremities of the flexible conductors carry silver contact elements which are actuated to progressively contact each other by the pivoted prod P connected to the solenoid plunger. Movements of the solenoid plunger are opposed by the tension spring, which biases the prod to open the contacts of the regulator. In the first instant of field discharge the solenoid responds to the discharge voltage peak and shunts the entire resistor R2 from the discharge circuit through the medium of the closed regulator contacts. As the discharge voltage drops and the magnetic pull of the solenoid tends to relax, the tension spring overcomes the magnetic pull sufiicientiy to open some of the contacts and insert resistance. The progressive insertion of resistance in the field discharge circuit continues until the field is completely discharged. The curves of Figs. 5 and 6, in general principle, are illustrative of the control characteristics of this embodiment also.

Yet another equivalent of the invention in Fig. 1 appears in Fig. 4. Here a mercury controlled device M replaces the regulator SR of Fig. 3. It carries a plurality of spaced contact discs stacked between insulating segments. The discs are connected along spaced taps of the resistors R2. A hole extending through the assembly terminates in a reservoir at the top end of the device M and in a bellows at the bottom, in which bellows the mercury is normally carried. The solenoid S, again energized by the discharge voltage when the back contacts of FSZ close, compresses the bellows B and forces mercury through the entire length of the hole. As the field discharge voltage drops the magentic pull of the solenoid relaxes and the forces of the biasing spring removes the compression force against the bellows causing it to expand. As a consequence the mercury level in the hole falls and progressively disengages the contact discs from top to bottom until the field discharge is complete.

There are, of course, many other electrical equivalents of the particular arrangements illustrated in the drawings. There are, further, other variants'of the circuit schemes illustrated which embrace the principles set forth in the drawings and the specification. It is, therefore, intended that the foregoing disclosure and the showing made in the drawings be considered only as illus- 5 trative of the principles of this invention and not be interpreted in a limiting sense.

I claim as my invention:

1. In a field discharge system for a dynamo-- electric machine having a field winding'energized from a source of electrical energy, the combination of, resistance means for forming a discharge circuit for said field Winding, a first switch for connecting and disconecting said field winding and said source of electrical energy, a second switch for. connecting and disconnecting said resistance means across said field winding, operating means for both of saidswitches for closing saidLsecond switch prior to opening of saidlfirst switch, electromagnetic means for decreasing the ohmic value of said resistance means, mechanical biasing means opposing said electromagnetic means for increasing the ohmic value of said resistance means, and circuit means connecting said electromagnetic means to be energized in dependence of the voltage of said field winding.

2. In combination, a generator having armature windings adapted for connection to a load and field winding means for exciting the generator adapted to be energized from a source of electrical energy, a carbon pile resistance element, a first switch for connecting and disconnecting said field winding means and said source of electrical energy, a second switch for connecting and disconecting said carbon means, operating means for both of said switches for closing said second switch prior to opening of said first switch, an electromagnetic device having an operating coil and a magnetically operated member, means for connecting said operating coil to be energized according to the voltage drop across said carbon pile resistance element, and means for transmitting the movements of said magnetically operated member to said carbon pile element to vary the pressure forces thereon.

3. In a field discharge system for a dynamoelectric machine having a field winding adapted to be energized from a source of electrical energy, the combination of, resistance means for forming a discharge circuit for said field winding, a first switch for connecting and disconnecting said field winding and said source of electrical nergy, a second switch for connecting and disconnecting said resistance means across said field winding, operating means for both of said switches for closing said second switch prior to opening of said first switch, electromagnetic means for changing the ohmic value of said resistance means, mechanical biasing means opposing said electromagnetic means for changing the ohmic value or said resistance means in an opposite sense, circuit means connectin said electromagnetic means to be energized in dependence of the voltage of said field winding, and means for damping the movements of said electromagnetic and mechanical means.

4. In a field discharge system for a dynamoelectric machine having a field winding adapted to be connected to a source of electrical nergy, the combination of, resistance means i or forming a discharge circuit for said field winding, a first switch for connecting and disconnecting said field Winding and said source or" electrical energy, a second switch for connecting and disconnecting said resistance means across said field winding, operating means for both of said switches for closing said second switch prior to opening of said first switch, electromagnetic means for increasing the ohmic value of said resistance means, mechanical biasing means opposing said electromagnetic means for decreasing the ohmic value of said resistance means, a relay energized'by the voltage across said field winding, circuit means operated winding, a first switch for connecting and disconnecting said field winding and said source of-electrical energy, alsecond switch for connecting and disconnecting said resistance means across said field winding, operating means for both of said switches for closing said second switch prior to opening of said first switch, a regulating device comprising a plurality of spaced flexible electrical conducting members each having contacts adjacent an extremity thereof disposed in cooperating spaced relation to the contacts of adjacent conducting members, said conducting members upon deflection engaging adjacent contacts, circuit means connecting the remaining extremities of said conducting members along spaced taps of said resistor whereupon progressive deflection of said conducting members and progressive engage- :ment of said contacts progressively shunts said tapped portions of said resistor, an electromagnetic device connected in parallel with said resistor to be energized in dependence of the voltage thereof for deflecting said conducting members and engaging said contacts, and biasing means for opposing the operation of said electromagnet.

6. In a field discharge system for a dynamoelectric machine having field winding means energized from a source of electrical energy, the combination of, a resistance regulating device for forming a discharge circuit for said field winding, a first switch for connecting and disconnecting said field winding and said source of electrical energy, a second switch for connecting and dis- 7 connecting said resistance means across said field winding, operating means for both of said switches for closing said second switch prior to opening of said first switch, mechanical means operable in each of two directions for operating said resistance regulating device to control the resistance thereof, an electromagnetic device for actuating said mechanical means in one of said two directions, means opposing the operation of said electromagnetic device, and circuit means for energizing said electromagnetic device in dependence of the voltage of said field winding.

7. In combination, a dynamoelectric machine having armature windings and a separately eX- cited field winding and circuit therefor, a field switch for opening and closing the field winding circuit, field discharge resistance means, a field discharge switch for connecting and disconnecting said field discharge resistance means across said field winding, operating means for actuating both of said switches, said operating means closing said field switch after opening of said field discharge switch and closing said field discharge switch prior to opening of said field switch, electromagnetically operated biasing means for changin the resistance of said field discharge resistance means, mechanical biasing means opposing said electromagnetically operated biasing means, and circuit means connecting said electr magnetically operated biasing means in parallel with said field discharge resistance means.

8. A protective circuit for a generator having armature windings and a field winding and a circuit therefor comprising, in combination, field discharge resistance means for forming a field discharge circuit for said field winding, switching means operable in one position to close the circuit for said field winding and open said field discharge circuit and operable in a second position to close said field discharge circuit prior to opening of said circuit for said field winding, electromagnetic means connected across said field discharge resistance means for changing the resistance thereof, mechanical means for opposing said electromagnetic means and changing the resistance of said field discharge resistance means in an opposite sense, and electrical means electrically connected to the armature windings of said generator for effecting movement of said switching means to said second position.

JAMES F. YOUNG.

file of this patent:

UNITED STATES PATENTS Name Date Rady Nov. 9, 1948 Number 

